High speed, high efficiency optical pattern generator using rotating optical elements

ABSTRACT

An optical pattern generator includes one or more multi-faceted rotating optical elements that introduce an offset that is rotation insensitive. The component that generates the offset is rotationally symmetric around the rotational axis of the optical element. Thus, as the optical element rotates, the effect of the offset component does not change. In addition, rotating optical elements may be designed to counteract unwanted optical effects of each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/750,790, filed on Dec. 31, 2003, now U.S. Pat. No. 7,184,184,entitled “High Speed, High Efficiency Optical Pattern Generator UsingRotating Optical Elements” and is related to U.S. patent applicationSer. No. 11/339,097 filed on Jan. 24, 2006, entitled “High Speed, HighEfficiency Optical Pattern Generator Using Rotating Optical Elements,”the entire disclosures of which are both hereby incorporated byreference herein in their entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to optically generating a pattern offigures, such as an array of spots or an array of scan lines. Moreparticularly, this invention relates to generating such patterns usingmulti-faceted rotating optical elements.

2. Description of the Related Art

The optical generation of a pattern of spots or scan lines is used in avariety of applications. Digital copiers, printers, fingerprintidentification, hand-held bar code scanners, industrial applications,light show entertainment, displays, telecommunications switching andmedical applications are a few examples. Perhaps the most commonmechanisms for generating patterns of figures are tilting mirrors (e.g.,oscillating mirrors driven by galvanometers) and reflections fromrotating polygons.

However, optical pattern generators based on tilting mirrors typicallyhave characteristics that make them unsuitable for certain applications.For example, scanning in these systems is typically achieved by tiltinga mirror back and forth. But back and forth motion requires that themirror come to a stop and then reverse direction. This takes time, whichlimits the scan rate. In order to increase the scan rate of thesesystems, the mirror often is driven with an oscillating motion at a ratethat is near its resonant frequency. However, this severely restrictsthe patterns that can be generated. For example, it is difficult togenerate irregular patterns since the mirror motion is constrained to beoscillatory. The near-resonance condition also limits the range of scanrates that can be achieved. For example, it is difficult to tune such asystem over a wide range of scan rates since the near-resonancecondition cannot be met over a wide range. If a two-dimensional patternis desired (e.g., a series of parallel scan lines or a two-dimensionalpattern of spots), then typically either a single mirror is tilted intwo directions simultaneously or two coordinated, tilting mirrors areused. In many cases the efficiency of the utilization of light, such aslaser light, is also important. The efficiency may be defined as thefraction of energy deposited in a desired pattern on the treatmentsurface compared to the total energy produced by the light source in agiven period of time. If a pattern is sparse compared to the background,it is preferable to turn off the light source and scan quickly over thebackground, and then turn it back on when the light beam has settledover the spot to be exposed and expose the spots in the pattern in sucha manner that the light source is efficiently utilized in time. Thisrequires an even more responsive device that can accelerate, decelerateand settle quickly. As a result of these characteristics,galvanometer-based systems are not well suited for high speed patterngeneration, particularly if the pattern is an irregular or a sparse one.

In the rotating polygon approach, the sides of a three-dimensionalpolygon are mirrored and the polygon is rotated about a center axis. Aseach mirrored side rotates through an incident optical beam, the opticalbeam is reflected to generate a point on a scan line. The rotation ofeach mirrored side through the optical beam produces one scan line. Ifall of the mirrored sides are the same (e.g., make the same pyramidangle with the base of the polygon), then the same scan line is tracedover and over. If the mirrored sides are different, then different scanlines can be traced as each side rotates through the optical beam. Forexample, by varying the pyramid angle of each side, the reflectedoptical beam can trace a series of scan lines.

However, the rotating polygon approach also has drawbacks that make itunsuitable for certain applications. For example, systems that produce aseries of scar lines can suffer from aberrations due to the rotation. Inorder to trace a series of scan lines, each side has a different pyramidangle that offsets the basic scan line in a direction that isperpendicular to the scan direction. However, as each side rotatesthrough the optical beam, the orientation of the angled side is alsorotated. This can cause changes in the amount of offset and/or otherunwanted aberrations. One example is scan line bow. The ideal scan lineis generally a straight line segment but the actual scan line is oftenan arc segment. The sag of the arc segment is the bow. In the case ofrotating polygon scanners, sides that have non-zero pyramid anglesgenerate bowed scan lines. The amount of bowing depends on the pyramidangle. In a polygon scanner where different pyramid angles are used totrace multiple scan lines or to generate spots at different locations,not only will each scan line be bowed, but the bow will vary from onescan line to the next. The difference between the bow of the top-mostscan line and the bottom-most scan line can be significant.

Scan line bow and other effects caused by rotation can cause additionalproblems, depending on the application. For example, in someapplications, the scanning action is used to compensate for motion ofthe scanner relative to a target so that the optical beam ideallyremains at a fixed spot on the target even though the scanner is movingrelative to the target. In this case, scan line bow will cause theoptical beam to move in the direction perpendicular to the scandirection. If this motion is slow compared to the dwell time of theoptical beam on the target, then the bow effectively introduces anunwanted motion in the perpendicular direction. If the motion is fastrelative to the dwell time of the optical beam on the target, then thebow, which is a radial deflection, when combined with the uncompensatedtangential motion, effectively blurs the optical beam, increasing thespot size of the beam on the target. Typically, neither effect isdesirable.

Thus, there is a need for optical pattern generators than can operate athigh speeds, particularly for the generation of irregular patterns.There is also a need for pattern generators with reduced aberrationsand/or blurring.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art in anumber of ways. In one aspect, one or more multi-faceted rotatingoptical elements introduce an offset that is rotation insensitive. Thecomponent that generates the offset is rotationally symmetric around therotational axis of the optical element. Thus, as the optical elementrotates, the effect of the offset component does not change.

In another aspect, two or more multi-faceted rotating optical elementsare used to counteract unwanted effects produced by each other. In oneexample, one rotating optical element introduces a deflection but alsosome unwanted optical power. A second rotating optical elementcounteracts the optical power while reinforcing the deflection. Theresult is a deflected beam with no additional optical power. In anotherexample, the rotating optical elements generate scan lines and the scanline bow introduced by one rotating optical element counteracts the bowintroduced by other rotating optical elements, while reinforcing thedesired scan.

In one embodiment, an optical pattern generator includes a multi-facetedrotating optical element having a plurality of facets. Each facet causesan incident optical beam to generate a figure (e.g., a spot or a scanline) as the facet rotates through the optical beam. The facets togethergenerate an array of figures. One or more facets include an offsetcomponent that is substantially rotationally symmetric and substantiallycentered on the rotational axis of the rotating optical element. Theoffset component offsets the figure along an offset direction, which isgenerally aligned with a radial direction of the rotating opticalelement. In one implementation, different facets offset the figures bydifferent amounts. The facets can be arranged so that the figures areoffset by uneven amounts and/or generated in a non-sequential order. Insome embodiments, the figure can be more complex than a spot or a scanline and the figure can vary over time. In addition, the patterngenerator can be combined with another motion or scanning mirror. Theresulting pattern can be a changing two-dimensional image, such as in avideo display.

In a particular design, there are two counter-rotating scan disks withone-to-one correspondence of facets. For at least one pair ofcorresponding facets, the facets on both scan disks include an offsetcomponent as described above. The offset components are implemented as apositive lens-like element on one scan disk and a negative lens-likeelement on the other scan disk. In some applications, the powers of thelens-like elements vary from facet to facet, with different facetsintroducing different offsets. The facets may also include scancomponents to generate a scan line, for example with the scan componenton one facet introducing a bow that counteracts the bow introduced bythe scan component on the other facet.

In another aspect, an optical pattern generator deflects an optical axisalong an array of scan lines. The optical pattern generator includes twomulti-faceted rotating optical elements, with one optical elementlocated downstream of the other. The two rotating optical elements arecounter-rotating and have corresponding facets. The facets cause theoptical axis to deflect along a scan line as the facets rotate throughthe optical axis. The optical elements may also implement bow correctionand/or offset of scan lines, as described above. This type of patterngenerator can be used in many different applications, including bothsystems that generate optical figures and imaging systems.

In another aspect, different devices include various combinations of theoffset functions, scan line functions and counteracting principlesdescribed above. In some embodiments, rotating optical elements arecombined with conventional scanners. Other aspects of the inventioninclude methods corresponding to the devices described above, andapplications for all of the foregoing, including for example using thescan lines to compensate for motion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be morereadily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a side cross section of an optical pattern generatoraccording to one aspect of the invention.

FIG. 1B is a perspective view of the optical train of the patterngenerator of FIG. 1A.

FIG. 1C is a diagram illustrating offset of scan lines.

FIG. 2 is a ray trace through two offset components.

FIG. 3A is a diagram illustrating an offset pattern.

FIG. 3B is a top view of a scan disk used to generate the offset patternof FIG. 3A.

FIG. 4A is a top view of the rotating optical elements of the patterngenerator of FIG. 1.

FIG. 4B is a diagram illustrating bow correction in a scan line producedby the rotating optical elements of FIG. 4A.

FIG. 5A is a perspective view of another pattern generator according tothe invention.

FIG. 5B is a ray trace through the pattern generator of FIG. 5A.

FIG. 6 is a ray trace through another pattern generator according to theinvention.

FIGS. 7A-7C are diagrams illustrating various patterns generated bysystems using a pattern generator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1C illustrate one example of an optical pattern generator 100according to the invention. The optical train of the pattern generator100 includes one or more optical sources 110A-E and one or moremulti-faceted rotating optical elements 120A-B. It may also includeadditional optics 130A-B for shaping the optical beam(s) as they passthrough the optical train to the target surface 150.

The optical source 110 produces an optical beam(s) that is incident uponthe rotating optical elements 120. Each rotating optical element 120 hasa number of facets, and facets on one rotating optical element 120 havecorresponding facets on the other optical elements 120. The rotation ofthe optical elements 120 is synchronized so that corresponding facetsrotate through the incident optical beam in synchronization.

The optical beams generate FIGS. 140A-E on the target surface 150 as thefacets rotate through the optical beams. In this example, the FIGS.140A-E are scan lines, although they can be spots or other shapes inalternate embodiments. In FIG. 1A, the scan direction 142 is in and outof the paper. The facets also offset the scan lines 140 in a direction144 perpendicular to the scan direction 142. For example, referring toFIG. 1C, one set of corresponding facets on the scan disks may producethe set of scan lines 140A-E, with each of the five scan lines traced bythe corresponding optical beam. The next set of corresponding facets mayproduce the scan lines 141A-E, which is offset by an amount Δ relativeto the scan lines 140.

For convenience, the portions of the facets that cause the optical beamsto trace the scan lines shall be referred to as scan components and theportions that cause the offset of the scan lines shall be referred to asoffset components. These may be implemented as physically distinctcomponents, for example the scan component can be attached to one sideof the optical element 120 and the offset component to the reverse side.Alternately, they may be integrated into a single component. Forexample, a general asphere may be used, with the asphere implementingboth the scanning and the offset functions. Alternatively, the scanningand offset functions can be generated by a spherical surface that hasits axis of symmetry slightly displaced from the axis of rotation of thedisk to which it has been mounted. In addition, this example patterngenerator has both scanning and offset, but alternate embodiments mayutilize only scanning or only offset.

In the specific example shown in FIG. 1, five optical fibers are used asthe optical sources 110. Collimation optics 130A collimate the opticalbeams from the five fibers. Two scan disks 120A-B are located in closeproximity to plane 160, one on each side of the plane. Plane 160 iswhere the chief rays of the five optical beams cross. The rotationalaxes 125 of the scan disks are located on opposite sides of the opticalbeams. The scan disks 120 are counter-rotating (i.e., if one rotatesclockwise, the other rotates counter-clockwise) so that correspondingfacets generally travel together as they rotate through the opticalbeam. Focusing optics 130B refocus the deflected collimated beams tospots on the target surface 150. The spots trace out scan lines 140 dueto the scanning action of the facets, and the scan lines are offset dueto the offset action of the facets. Motors rotate the scan disks 120.

FIG. 2 illustrates the offset component of the facets. In a conventionalapproach, the offset component that generates the offset may be a prism.However, as the scan disk rotates, the prism also rotates and this canintroduce unwanted effects, such as unintentional scanning of theoptical beam. To avoid this effect, the offset components in thisexample are rotationally symmetric about the rotational axis of therespective optical element 120. Then, when the optical element 120rotates, there is no change in the optical effect of the offsetcomponent. One example of such an offset component is a portion of asphere, where the axis of the sphere is aligned with the rotational axisof the scan disk. Spheres with a shorter radius result in a greateroffset of the spherical surface at the centerline of the optical beam.

FIG. 2 illustrates a specific example of a rotationally symmetric offsetcomponent. In this case, the offset components on the two scan disks120A-B are lenses 320 centered about the respective rotational axes125A-B of the scan disks. The offset components have optical powers thatare equal in magnitude but opposite in sign, and the optical beam 210 islocated midway between the two rotational axes 125. In FIG. 2, theoffset component 320A is a lens with negative (divergent) optical powerand offset component 320B is a lens with positive power.

Due to the diverging nature of the lens 320A, after passage through thislens, the light appears to radiate from a point source located on therotational axis of the lens (which in this case is also the rotationalaxis 125A of the scan disk). Since the optical beam 210 has a smalldiameter relative to the lens 320A, this effect is primarily adeflection of the optical beam 210 away from the rotational axis 125A.In addition, the individual light rays in the optical beam begin todiverge away from each other and, if allowed to propagate a longdistance, the optical beam would begin to broaden. However, the opticalbeam very soon reaches the second offset component 320B, which has anoptical power that is very nearly equal and opposite to that of thefirst. The optical beam emerges essentially collimated. In addition,since the rotational axis 125B of the positive lens 320B is on theopposite side of the optical beam as the axis 125A for the negative lens320A, the deflection imparted by the second lens 320B adds to thedeflection imparted by the first lens 320A. The net result is that theincoming collimated beam leaves the two scan disks 120 still collimatedbut deflected by a certain amount. Furthermore, this amount ofdeflection and the shape of the outgoing beam do not change as the scandisks 120 rotate since the offset components are rotationally symmetricabout the axes of rotation.

FIG. 2 shows the lenses 320A and 320B as entire lenses. This was donefor illustrative purposes. In the actual implementation, each lens 320does not cover the entire scan disk 120. Rather, each lens covers afacet on the scan disk. Different facets can use lenses of differentpowers. For example, one pair of corresponding facets may contain astrong positive lens and a strong negative lens, thus causing a strongdeflection. The next pair of corresponding facets may contain a weakerpositive lens and a weaker negative lens, thus causing a weakerdeflection. As the different pairs of facets rotate through the incidentoptical beam, the beam is deflected by different amounts due to thedifferent optical powers in the lenses. However, the beams all emergecollimated. Thus, focusing optics can be used to focus the emergingbeams onto a flat target field.

The use of multi-faceted rotating optical elements to implement theoffset has significant advantages, some of which are illustrated inFIGS. 3A-3B. FIG. 3A shows the offsets 341-349 to be generated. Notethat FIG. 3A is a depiction of the offset pattern. If the figuresgenerated by the system are spots, then an array of offset spots will begenerated. If the figures are scan lines, then an array of offset scanlines will be generated. If multiple optical beams are used (as in FIG.1), then the basic pattern will be replicated. If a more complex objectsource which changes in time is used, the image of that source will bereplicated and will change in time. FIG. 3B shows one of the pair ofrotating optical elements used to generate these offsets. The rotatingoptical element has facets 361-369 and so on.

One advantage is that each offset 141-149 is generated by acorresponding pair of facets 361-369, but the facets can be designedindependently of each other. Therefore, the offsets can be unevenlyspaced, as shown in FIG. 3A. In addition, the figures can be generatedin a non-sequential order. That is, it is not required that facet 361generates offset 341, facet 362 generates offset 342, facet 363generates offset 343, etc. Instead, facets 361-369 might generateoffsets 341, 344, 347, 342, 348, 343, 345, 349, and 346, respectively.As the facets rotate through the optical beam, the figures will begenerated in this non-sequential order. Figures can also be multiplyexposed by adding corresponding facets. For example, facets 361, 364 and367, might all generate offset 344. This characteristic allows thegeneration of irregular patterns. Irregular two-dimensional patterns canbe generated by using two crossed systems, one causing deflection in thex direction and the other causing deflection in the y direction.Alternately, this approach can be combined with an ordinary galvanometermirror or polygon mirror scanner to create two-dimensional patterns.

Another advantage is the speed of this approach. Disks can be rotated atvery high speeds. For example, if a disk contains 30 facets and rotatesat a speed of 10,000 rpm, then the system will generate 5,000 figuresper second, if there is a single beam source. If the source has N beams,5,000N figures per second will be generated. Furthermore, the speed canbe varied over a wide range since there is no requirement to stay near aresonant frequency. In one approach, the drive shafts or the disksthemselves are encoded and this feedback is used to both control thespeed of the disks and to synchronize the disks with each other.

If the offset component is exactly rotationally symmetric and exactlycentered on the rotational axis of the optical element, then the offset,which will be in the radial direction, will not vary as the offsetcomponent rotates through the optical beam. If there are no othercomponents on the facet, then the system will generate an array of spotsoffset in the radial direction.

In many applications, however, it is advantageous to break the exactrotational symmetry. For example, a small amount of asymmetry may beadded to the offset component in order to correct other aberrations.Alternately, the offset component may be slightly decentered from therotational axis of the optical element, for example to introduce ascanning motion. Any scanning motion can be broken into a radialcomponent and a tangential component. The symmetry in FIG. 2 allows thetwo disks to be designed so that the radial components fromcorresponding facets cancel and the tangential components reinforce. Forexample, if the two lenses 320A and 320B have the same (but opposite)power, they can be decentered by the same amount relative to theirrotational axes 125, toward one another or away from one another. Theresult is a scan line that is purely in the tangential direction sincethe radial scan effects from the two lenses 320 cancel.

FIGS. 4A-4B further illustrate how facets can be designed so that theirradial scan effects cancel. Scan components generally introduce a bow inthe scan line as they rotate through the incident optical beam. In thiscase, while the scan component on each scan disk may introduce a bow,the two scan components are designed so that the different bowscounteract each other and the overall bow is reduced or eliminated.

One example of a scan component is an off-center lens. In general, anoff-center lens will produce a change in ray direction proportional tothe amount of decenter. That is, Δθ=δx/f where Δθ is the change in raydirection, δx is the amount of decenter and f is the focal length of thelens. Thus, a scan line can be created by moving a lens through anoptical beam.

Referring to FIGS. 4A-4B, assume for the moment that there is only onescan disk 120A, that the optical beam 210 is normally incident to thescan disk 120A and that the scan component of the current facet has thesame optical effect as a lens with positive optical power (negativepower lenses can also be used), as represented by the circle 220. Thecircle representation is not meant to imply that the scan component mustbe circular in shape. For example, it may have the same shape of thefacet. The optical beam is initially directed to the center of thecircle 220. As the facet rotates through the optical beam 210, thecenter of the circle 220 also rotates about the rotational axis 125A.The resulting scan line follows the motion of the lens, tracing out anarc 240A as shown in FIG. 4B. The sag of the arc is the bow of this scanline.

This bow can be reduced, or even eliminated, as follows. If the scancomponent on scan disk 120B is also a lens with positive optical power,it will trace the arc 240B. But this arc is bowed in the oppositedirection as arc 240A. The two bows counteract each other, resulting ina net scan line 245 that scans faster and is longer and with less bow.In some cases, the bow can be entirely eliminated. For example, thiswill be the case if the scan disks 120A-B are in close proximity to eachother (so that propagation between the scan disks has negligibleeffect), the distance from the optical beam 210 to each rotational axis125 is the same, and both scan components are lenses with the sameoptical power located in the same relative position on their respectivefacets.

Note that the offset generation and scan line generation were describedabove using specific examples. This was done for purposes of clarity andthe invention is not limited to these examples. For example, it is notlimited to either a single optical beam (e.g., FIG. 1 shows a case withfive optical beams) or a single facet or exactly the same facetreplicated over the entire scan disk. Each scan disk 120 containsmultiple facets and each set of corresponding facets produces a figure(e.g., a spot or a scan line). If the facets on a scan disk are all thesame, then the same figure will be repeated over and over with the sameoffset.

But the facets can also be different in order to produce differentfigures or figures with different offsets. For example, different scancomponents can be used on different facets in order to generatedifferent lengths of scan lines. Similarly, different offset components(e.g., lenses with different optical power) can be used on differentfacets in order to generate different offsets. Furthermore, scancomponents and offset components can be combined in various ways toachieve different scan patterns. In addition, the bow correction andoffset components described above need not be used with every facet. Forexample, a particular facet(s) may be designed for zero offset, in whichcase offset components are not necessary. Or there may be a set of Ndifferent offsets used for the entire pattern, with one of the N offsetsbeing zero. In that case, a majority of facets but not all facets mayutilize offset components. In some applications or for some facets, theundesirable effects introduced by conventional techniques may betolerable so that bow correction and/or offset techniques are notnecessary. At the other extreme, in some applications, every facet mayutilize the bow correction and/or offset components described above.

The physical implementations of the scan component and offset componentcan also vary. For facets that include a separate scan component andoffset component, different designs can place these components indifferent orders within the optical train. The scan component and offsetcomponent can also be integrated into a single optical component. Forexample, in the lens-based designs described above, the scan componentis implemented as a lens centered at approximately the same radiallocation as the optical beam and the offset component is implemented asa lens centered on the rotational axis of the scan disk. To a firstapproximation, the net effect of these two lenses is the same as that ofa single lens that has an optical power approximately equal to the sumof the optical powers of the scan component and the offset component andcentral axis that is located elsewhere. Thus, the two components can beimplemented as a single lens. Although it is usually desirable for theincident beam and the beam exiting the counter rotating disks to becollimated, that is not a requirement for practical use, since theobjective lens that focuses the exiting beam can be modified toaccommodate power in the scanned beams. In some instances even differentamounts of power from the different facet sets can be accommodated.

Furthermore, the examples shown above use transmissive facets butreflective or hybrid designs can also be used. The scan components andoffset components can also be based on refraction, reflection,diffraction or a combination of these. Mirrors, conventional lenses,aspheres, Fresnel lenses, kinoforms, diffractive and holographic opticsare examples of possible physical implementations. The term “lens-likeoptical element” will be used to refer to refractive lenses, curvedmirrors, holographic lenses and other optical elements that arecounterparts to refractive lenses.

FIGS. 5A-5B illustrate a reflective design. In this example, the opticalsource is a fiber laser at a wavelength of 1535 nm. Collimation optics130A collimate the incoming optical beam onto two reflective rotatingscan disks 120A-120B, which are tilted at 19 degrees from normal. Eachscan disk 120 is approximately 30-50 mm in diameter with 15-30 facetseach. The facets typically extend roughly 5 mm in the tangentialdirection and slightly less than that in the radial direction. Theincident optical beam is approximately 1.0-1.5 mm in diameter. Thefocusing optics 130B includes a triplet for focusing the deflectedoptical beam onto the target. FIG. 5 show the optical beam at fivedifferent offsets 541-545. There are 15-30 offsets (one for each facet),that are evenly spaced approximately 0.75 mm apart, for a full targetwidth of about 15 mm.

This particular example is designed for the medical applicationdescribed in co-pending U.S. patent application Ser. No. 10/367,582,“Method and Apparatus for Treating Skin Using Patterns of OpticalEnergy,” filed on Feb. 14, 2003, and Ser. No. 60/486,304, “Method andApparatus for Fractional Phototherapy of Skin,” filed on Jul. 11, 2003,both of which are incorporated herein by reference. In this application,the optical scanner is swept over the skin. The scanning motion is inand out of the paper in FIG. 5. The actual scan line is short, typically0.1 mm, and is used primarily to compensate for the sweeping motion.Alternate embodiments utilize scan lines less than 1 mm. As a result,the optical beam remains focused on a single point on the skin for thescan duration of a single facet. For further details concerning themotion compensation, see co-pending U.S. patent application Ser. No.10/745,761, “Method And Apparatus for Monitoring and ControllingLaser-Induced Tissue Treatment,” filed on Dec. 23, 2003 and incorporatedherein by reference. When the next facet enters the optical beam,another treatment spot is generated at a different location. The disks120 are designed to rotate up to 6000 rpm, resulting in a treatment rateof up to 3000 spots per second.

FIG. 6 is an example of an optical pattern generator using one rotatingoptical element. The incoming optical beam arrives via an optical fiber110 and is collimated by collimation optics 130A. The collimated beam isincident upon the rotating optical element 120. The optical element 120is depicted as a lens in FIG. 6 in order to illustrate the offsetfunction. In reality, the optical element 120 contains approximately 20facets, each of which has an offset component that is implemented as alens centered on the rotational axis 125. Each lens has a differentpower and deflects the incoming optical beam by a different amount. FIG.6 shows all twenty of the deflected beams 641-649. The weakest lensgenerates the least deflected beam 641 and the strongest lens generatesthe most deflected beam 649. However, the different power lenses alsointroduce different amounts of focusing to each of the beams 641-649. InFIG. 2, this was counteracted by a second lens of equal but oppositepower. In this example, an echelon type mirror array 632 is used toindividually redirect each beam 641-649 to the target and a lens array634 individually focuses each beam 641-649 on the target 150.

Although the description above contains many specifics, these should notbe construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. Forexample, applications other than the medical application described abovewill be apparent, including a variety of laser materials processingapplications, printing/copying, laser display systems and direct markingof materials. The specific design of the optical pattern generator willdepend on the application. For example, the wavelength of the opticalbeams will depend in part on the application. Even just withindermatology, lasers having different wavelengths are used in differentsurgical applications. Examples of dermatology laser light sourcesinclude diode lasers, diode-pumped solid state lasers, Er:YAG lasers,Nd:YAG lasers, argon-ion lasers, He-Ne lasers, carbon dioxide lasers,excimer lasers, erbium fiber lasers, and ruby lasers. These devicesgenerate laser beams having the wavelength in the visible range of thespectrum (0.4-0.7 μm) as well as in infrared (0.7-11 μm) and UV(0.18-0.40 μm) ranges. It should be noted that terms such as “optical”and “light” are meant to include all of these and other wavelengthregions and not just the visible range of the spectrum.

Depending on the application, the figures generated can also takedifferent forms. In many applications, a single continuous scan line istraced repeatedly. In some applications, a series of parallel scan linesis produced, laterally offset from each other. The scan lines can alsobe a series of points rather than a continuous line, for example if asource laser is pulsed on and off during scanning. As a final example,scanning can also be used to compensate for motion so that the scan spotremains in a fixed position on a target even though the scanning deviceis moved relative to the target. Other variations will be apparent.

As another example of different variations, the number of rotatingoptical elements 120 can also vary. The above examples (other than FIG.6) all use a pair of scan disks but this is not a requirement. Forexample, two or more pairs of rotating optical elements can be used. Asanother example, the two-disk designs can be converted to three-diskdesigns by “splitting” one of the scan disks into two scan disks. InFIG. 3, the positive lens 320B can be split into two positive lenseswith half the power, one placed upstream of the negative lens 320A andthe other placed downstream of the negative lens 320A.

The basic pattern generator can also be used in many differentapplications. The rotating optical elements introduce a deflection tothe optical axis of the overall system. If the facets include offsetcomponents, then the deflection includes an offset generally along aradial direction. If the facets include scan components, then thedeflection includes a scan line, typically along a tangential direction.For example, a system that uses a 20 mm focal length objective lens witha 1 mm scan line will introduce a deflection of 0.05 radians. Differentapplications can use either or both of these, possibly in combinationwith other deflection mechanisms.

For example, FIGS. 7A-7C illustrate different patterns that can begenerated by systems using a pattern generator. In FIG. 7A, the patterngenerator is optically coupled to another scanning device, such as aconventional polygon scanner. The conventional scanning device alonewould generate a scan line, such as 711. The pattern generator generatesa pure offset (no scanning), as depicted by the offsets between the scanlines 711-714. The pattern generator operates at a much faster rate thanthe other scanning device. Thus, the set of offsets is cycled throughmultiple times in the time required for the conventional scanner togenerate one scan line. The resulting pattern is a set of “dashes” 721as shown in FIG. 7A. Each dash 721 corresponds to one facet (or set ofcorresponding facets) rotating through an incident optical beam.

In the example of FIG. 7B, the facets on the pattern generator alsocontain a scan component that counteracts the scan produced by theconventional scanning device. Thus, the dashes 721 in FIG. 7A arecompressed into spots 722 in FIG. 7B. As each facet rotates through theincident optical beam, the scan component on the facet counteracts theconventional scanner, thus holding the optical beam at a fixed location.When the next facet rotates into place, the optical beam jumps to thenext location, which in this example also includes a lateral offset.

In FIG. 7C, the pattern generator does not introduce a lateral offset.Rather, the scan components in the pattern generator counteract theconventional scanner generating a row 711 of spots 722. When the row iscompleted, an offset is introduced (e.g., by another conventionalscanner) to generate a next row 712 of spots. In this way, a display canbe built.

As a final example, the optical pattern generator can also be used inimaging or sensing systems. In one case, the object source is located atthe focal plane of the scanner and the sensor (such as a CCD) is locatedat the opposite end of the scanner. For example, rather than using thescan components to compensate for the scanning from a conventionalscanner, the scan components can be used to compensate for the motion ofan object that is to be imaged. In effect, the scanning can be used fordeblurring in the image capture. Application can be found in streakcameras.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the invention but merely asillustrating different examples and aspects of the invention. It shouldbe appreciated that the scope of the invention includes otherembodiments not discussed in detail above. Various other modifications,changes and variations which will be apparent to those skilled in theart may be made in the arrangement, operation and details of the methodand apparatus of the present invention disclosed herein withoutdeparting from the spirit and scope of the invention as defined in theappended claims. Therefore, the scope of the invention should bedetermined by the appended claims and their legal equivalents.Furthermore, no element, component or method step is intended to bededicated to the public regardless of whether the element, component ormethod step is explicitly recited in the claims.

1. An optical pattern generator comprising two or more multi-facetedrotating optical elements, each multi-faceted rotating optical elementhaving a rotational axis and a plurality of facets that rotate aroundthe rotational axis; wherein the rotating optical elements havecorresponding facets that rotate through an optical axis insynchronization and at least two of the corresponding facets causeunwanted optical effects that occur for each facet acting alone but thatcounteract each other when the facets are acting together.
 2. Thepattern generator of claim 1, comprising exactly two counter-rotatingmulti-faceted rotating optical elements.
 3. The pattern generator ofclaim 2, wherein the two corresponding facets together generate adeflection of the optical axis and the two corresponding facetsintroduce unwanted optical powers that counteract each other.
 4. Thepattern generator of claim 2, wherein the two corresponding facetstogether generate a deflection of the optical axis and the twocorresponding facets introduce unwanted optical powers that partiallycounteract each other and together introduce a net residual opticalpower.
 5. The pattern generator of claim 2, wherein the twocorresponding facets together generate a scan line of the optical axisand the two corresponding facets introduce unwanted scan line bows thatcounteract each other.
 6. The pattern generator of claim 2, wherein thetwo corresponding facets together generate an optical effect along atangential direction and the two corresponding facets introduce unwantedoptical effects along a radial direction that counteract each other. 7.The pattern generator of claim 1, wherein the rotating optical elementsare capable of rotating at a speed of at least 5,000 rpm.
 8. A methodfor using an optical pattern generator comprising rotating a pluralityof facets around a rotational axis of each of two or more multi-facetedrotating optical elements; wherein the rotating optical elements havecorresponding facets that rotate through an optical axis insynchronization and at least two of the corresponding facets causeunwanted optical effects that occur for each facet acting alone but thatcounteract each other when the facets are acting together.
 9. The methodof claim 8, wherein the optical pattern generator comprises exactly twocounter-rotating multi-faceted rotating optical elements.
 10. The methodof claim 9, wherein the two corresponding facets together generate adeflection of the optical axis and the two corresponding facetsintroduce unwanted optical powers that counteract each other.
 11. Themethod of claim 9, wherein the two corresponding facets togethergenerate a deflection of the optical axis and the two correspondingfacets introduce unwanted optical powers that partially counteract eachother and together introduce a net residual optical power.
 12. Themethod of claim 9, wherein the two corresponding facets togethergenerate a scan line of the optical axis and the two correspondingfacets introduce unwanted scan line bows that counteract each other. 13.The method of claim 9, wherein the two corresponding facets togethergenerate an optical effect along a tangential direction and the twocorresponding facets introduce unwanted optical effects along a radialdirection that counteract each other.
 14. The method of claim 8, whereinthe rotating optical elements are capable of rotating at a speed of atleast 5,000 rpm.
 15. An optical pattern generator comprising two or moremulti-faceted rotating means, each multi-faceted rotating means having arotational axis and a plurality of facets that rotate around therotational axis; wherein the rotating means have corresponding facetsthat rotate through an optical axis in synchronization and at least twoof the corresponding facets cause unwanted optical effects that occurfor each facet acting alone but that counteract each other when thefacets are acting together.
 16. The pattern generator of claim 15,comprising exactly two counter-rotating multi-faceted rotating means.17. The pattern generator of claim 16, wherein the two correspondingfacets together generate a deflection of the optical axis and the twocorresponding facets introduce unwanted optical powers that counteracteach other.
 18. The pattern generator of claim 16, wherein the twocorresponding facets together generate a deflection of the optical axisand the two corresponding facets introduce unwanted optical powers thatpartially counteract each other and together introduce a net residualoptical power.
 19. The pattern generator of claim 16, wherein the twocorresponding facets together generate a scan line of the optical axisand the two corresponding facets introduce unwanted scan line bows thatcounteract each other.
 20. The pattern generator of claim 16, whereinthe two corresponding facets together generate an optical effect along atangential direction and the two corresponding facets introduce unwantedoptical effects along a radial direction that counteract each other.